The panel cited various individual traits that might affect the person’s vulnerability to substance addiction, including their physiology, psychology and social and economic pressures, but excluded those from the rankings, rating the substances only on the potential inherent in the drug.

I have added some data from more recent research into other drugs such Ritalin (used to combat Attention Deficit Hyperactivity Disorder in children) and SSRI (selective serotonin re-uptake inhibitor) anti-depressants, by the World Health Organisation and the Uppsala monitoring centre in Sweden – these items were not commonly prescribed in 1990, and therefore were not included original survey.